This invention relates to a method for the finish machining of the blade root structure of gas-turbine engine blades cast in a brittle material, such as titanium aluminide, and to a device for employing the method, i.e. for the positioning, fixation and clamping of the workpiece.
Precision-cast blades made of titanium aluminide are characterized by low weight and appropriate thermal resistance and are, therefore, employed in engines under the aspect of maximum weight reduction. However, the material used is very brittle which is disadvantageous in that the blade cannot be conventionally clamped at the reference points (K points) on the airfoil for the required post-casting machining of the blade root geometry, as the brittle material will fail under the high forces occurring during the machining process.
In a known method, the blades made of titanium aluminide are first removed from the feeder and runner structure adhering to them upon casting. The airfoil is then positioned at the reference points specified for subsequent machining of the blade root geometry and, in this defined position, embedded in low-melting material. In this embedding material, the blade is gently held for machining its root by suitable clamping means to preclude blade fracture. However, embedding of the airfoil for clamping the blade and melting and removal of the embedding material after machining incurs considerable effort, in particular under the aspect that embedding must be accomplished with high accuracy to enable the workpiece to be machined with maximum precision on the basis of the reference points specified for finish machining.